[Flang][OpenMP]Incorrect execution result when reduction-identifier(+) is used in REDUCTION clause

[ohno-fj]

Version of flang-new : 18.0.0(1c876ff5155c4feeb2b2885eb3e6abda17c4b7f4)

Using reduction-identifier(+) in REDUCTION clause results in incorrect execution.
The program is executed on 1 thread and expects a value of 11 for a.

The following are the test program, Flang-new, Gfortran and ifort compilation result.

ompds111_2.f90:

program main
  integer :: a
  call OMP_SET_NUM_THREADS(1)
  a=1
!$omp parallel reduction(+:a)
  a=10
!$omp end parallel
  print *,a
end program main

$ flang-new ompds111_2.f90 -fopenmp; ./a.out
 10
$

$ gfortran ompds111_2.f90 -fopenmp; ./a.out
          11
$

$ ifort ompds111_2.f90 -qopenmp; ./a.out
          11
$

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: None (ohno-fj)

``` Version of flang-new : 18.0.0(1c876ff) ```

Using reduction-identifier(+) in REDUCTION clause results in incorrect execution.
The program is executed on 1 thread and expects a value of 11 for a.

The following are the test program, Flang-new, Gfortran and ifort compilation result.

ompds111_2.f90:

program main
  integer :: a
  call OMP_SET_NUM_THREADS(1)
  a=1
!$omp parallel reduction(+:a)
  a=10
!$omp end parallel
  print *,a
end program main

$ flang-new ompds111_2.f90 -fopenmp; ./a.out
 10
$

$ gfortran ompds111_2.f90 -fopenmp; ./a.out
          11
$

$ ifort ompds111_2.f90 -qopenmp; ./a.out
          11
$

[kiranchandramohan]

We are reviewing reduction, specifically to handle cases like this. https://discourse.llvm.org/t/rfc-openmp-reduction-support/3367/10

[ohno-fj]

Thank you for your comments on the development status.

[kiranchandramohan]

This is fixed (possibly by #79308)

[llvmbot]

@llvm/issue-subscribers-flang-ir

Author: None (ohno-fj)

``` Version of flang-new : 18.0.0(1c876ff) ```

Using reduction-identifier(+) in REDUCTION clause results in incorrect execution.
The program is executed on 1 thread and expects a value of 11 for a.

The following are the test program, Flang-new, Gfortran and ifort compilation result.

ompds111_2.f90:

program main
  integer :: a
  call OMP_SET_NUM_THREADS(1)
  a=1
!$omp parallel reduction(+:a)
  a=10
!$omp end parallel
  print *,a
end program main

$ flang-new ompds111_2.f90 -fopenmp; ./a.out
 10
$

$ gfortran ompds111_2.f90 -fopenmp; ./a.out
          11
$

$ ifort ompds111_2.f90 -qopenmp; ./a.out
          11
$